1. Field of the Invention
The invention relates to a method of fabricating a flash memory device and, more particularly, to a method of fabricating a flash memory device, which can prevent lowering of reliability of the device during a process for forming drain contacts, while simplifying the process.
2. Brief Description of Related Technology
A flash memory device has the advantages of EPROM, having the programming and erase characteristics, and EEPROM, having the electrically programming and erase characteristics. The flash memory device achieves the storage state of one bit using one transistor and can be electrically programmed and erased.
Depending on the cell array structure, a flash memory device can be classified into a NOR type structure in which cells are arranged in parallel between bit lines and the ground and a NAND type structure in which cells are arranged in series between bit lines and the ground. Cell arrays of the NAND type flash memory device are connected by a string, unlike a general flash device. A drain contact connected to a bit line and a source line contact for a global ground are located at both ends of the string. The contacts are connected to junctions of a select transistor for string control.
A pattern process is generally performed to form the drain contact. For example, a plurality of hard mask layers are formed over a semiconductor substrate having an underlying structure that includes source contact plugs. A polysilicon layer is used as the hard mask layer. A bottom anti-reflective coating (BARC) layer is deposited on the polysilicon layer. Subsequent processes, including an exposure process and a development process, are then performed on a subsequently formed photoresist layer.
The stress of amorphous carbon formed below the polysilicon layer causes cracks to generate during deposition of the polysilicon layer, which may lower reliability of the device. As a result, process steps are added such as etching of the BARC layer and photoresist patterning, which increases manufacturing costs and time. Consequently, productivity decreases.